The present invention concerns control devices for stepping motors.
In stepping motors, the analysis of the voltage induced in the motor coil by the movement of the rotor makes it possible to ascertain the performance of the motor at the moment at which it performs a stepping motion. Such analysis may be useful both with regard to producing circuits for monitoring and controlling the motor, in particular those circuits which make it possible to adapt the duration of the driving pulses applied to the motor to the load it drives, and also with regard to equipment for measuring parameters of the motor, such as the working torque, current consumption, etc. or for monitoring proper operation of the motor.
Now, most stepping motors, more particularly those used in the timepiece industry, are supplied with fixed-voltage driving pulses. During these driving pulses, measurement of the induced voltage can then be effected only indirectly, by analysing the current in the coil. This operation is a delicate one, by virtue in particular of the influence of the self-inductance of the coil itself, which has a substantial inductance value and which opposes the variations in current resulting from the presence of the induced voltage, thereby disturbing the measurement.
Another disadvantage from which the known control devices suffer is due to the fact that, if the voltage of the supply source to which the coil is connected in the course of the driving pulses varies, the power applied to the motor also varies. Operation of the motor is therefore affected by the variations that may occur in the electromotive force and the internal resistance of the power source, as is the case in timepieces where the motor may be supplied by batteries, the voltage of which varies in dependence on time and from one type to another.